Genetic Analysis Clears Accused
Medics

A new molecular study provides the strongest scientific evidence yet that six foreign medics held in Libya are innocent of charges that they deliberately infected more than 400 children with HIV. Accumulated mutations in the virus genomes reveal that the outbreak began well before the medics arrived in the country. The Libyan supreme court is set to decide on 19 December whether to execute the medics. It is unclear whether the new study will influence its verdict.

International criticism of the Libyan government has intensified since October, when the country's supreme court refused to consider scientific evidence in the case against the medics (ScienceNOW, 24 October). Prosecutors charge that the medics--five Bulgarian nurses and one Palestinian doctor--infected 426 children at a hospital in Benghazi as an act of bioterrorism. But European scientists who gained access to the hospital's records in 2004 discovered that 32 of the infected children had been treated at the hospital before the accused medics had even arrived. Also, the diversity of viruses, which include several strains of hepatitis in addition to HIV, suggested a classic hospital outbreak due to poor hygiene practices rather than a deliberate inoculation from a single source.

The new genetic analysis of the viruses tells a similar story. A team led by Tulio de Oliveira & Oliver Pybus, an evolutionary biologist at the University of Oxford, U.K., obtained blood samples from 66 of the Libyan children who had been sent to European hospitals for care. They extracted and sequenced RNA from 41 strains of HIV as well as 61 strains of hepatitis C virus infecting the children. Because the viruses accumulate mutations as they reproduce and spread, differences between their genomic sequences can be used like a molecular clock to estimate how long ago they last shared a common ancestor. The more mutations that have accumulated in each strain, the longer back in time that the hospital outbreaks must have occurred.

The molecular evidence is solidly in favor of the medics' innocence, Pybus and his coauthors conclude. All of the analyses performed put the date of the outbreak well before the medics' arrival in Libya in March 1998, the team reports online today in Nature. For some strains of the hepatitis C virus, the most likely date of the original hospital infection was before 1995, indicating that poor hygiene practices--such as reuse of needles and improper sterilization techniques--have been causing accidental infections there for more than a decade. "I am persuaded," says Jeff Thorne, a molecular biologist at North Carolina State University in Raleigh who specializes in viral evolution. "This study shows that the accused medical staff are innocent beyond a reasonable doubt."